The following tables compare general and technical information for a number of instant messaging clients. Please see the individual products' articles for further information. External links may lead to extensions that add a feature to a client.

^The connection between the Google Talk client and the Google Talk server is encrypted, except when using Gmail's chat over HTTP, a federated network that doesn't support encryption, or when using a proxy like IMLogic. - Google

The following table is an overview of those Instant Messenger clients which, by default, provide both end-to-end encrypted messaging and unencrypted messaging (e.g. with contacts who do not have the application or with contacts who have a version of the application that does not support end-to-end encryption). The information in this table is only applicable to those conversations that are end-to-end encrypted.

The following table is an overview of those Instant Messenger clients which provide end-to-end encryption as an optional mode or setting that is not enabled by default. The information in this table is only applicable when the mode or setting is enabled. Some clients require the installation of a separately downloadable plugin.

^ abcFor transparency to the public, the source code of the encryptionalgorithms, and its implementation into a messenger, should be subject to public auditing—which may disclose flaws or implementation failures. Whereas, a company offering a messenger which does not reveal the source must be blindly trusted. In general it is recommended to not trust closed source encryption.

^ abcIf a messenger relies on a central server, the setup is closed and may be surveilled. To counter this, decentralized computing architectures have been developed via a peer-to-peer technology, open source chat servers (easily setup by anyone) and/or federated protocols. An architecture in which all the messages do not pass through a central server lessens a single point for surveillance.

^ abcThe clients have a built-in method for users to verify the identity of correspondents they are speaking with and the integrity of the channel, even if the service provider or other third parties are compromised. Two possible ways of doing this are through:

An interface for users to view the fingerprint (hash) of their correspondent's public keys as well as their own, which users can verify manually or out-of-band.

A key exchange protocol with a short-authentication-string comparison. An example is the Socialist millionaire's protocol.

The solution should verify a binding between the users and the cryptographic channel.

^ abcdefIn symmetric cryptography, the same key is used for encryption and decryption. Knowledge of this key needs to be limited to the two communication partners to ensure confidentiality. As asymmetric algorithms are relatively computationally costly in terms of speed, as compared to symmetric cryptography, the session key may be encrypted / decrypted by a asymmetric algorithm and use a much faster symmetric algorithm to encrypt and decrypt messages, reducing computational cost (increasing speed).

^ abcMultiple encryption is the process of encrypting an already encrypted message one or more times, either using the same or a different algorithm.

^ abcPublic keys are used to identify users. A user's IP address can in some cases be related to his or her public key. Messengers that do not relate the user's public key to the user's IP address are considered more secure. This offers more security because the IP cannot be targeted to gain access to the private key. If an attacker knows the IP related to a public key, he or she can try to get on the remote machine, download and decrypt the private key and thus decrypt all encrypted communication.

^ abcThe critical advantage in an asymmetric key system is that copies of keys do not need to be sent between communicators. This prevents a third party from copying a key while it is in transit, and preventing the third party from spying on all future messages. In addition, if one key was copied by a third party, only messages to the holder of the key would be compromised, not the messages to the other party in the communication. However, asymmetric algorithms are relatively computationally costly in terms of speed, as compared to symmetric cryptography. The most common asymmetric cryptography algorithm is the RSA Algorithm. Alternative asymmetric algorithms are Digital Signature Algorithm (DSA), Elliptic curve cryptography (ECC), ElGamal and NTRU. NTRU is regarded not vulnerable to decryption by quantum computing.

^ abcThe key size describes the length of the needed mathematical operation. Simply spoken, the longer the key, the longer it takes to crack it.

^Only one-to-one messages are end-to-end encrypted. Public chatrooms are not end-to-end encrypted.

^Signal contains a setting that allows users to send unencrypted SMS/MMS messages to contacts who do not have Signal. This setting is not enabled by default. Users can also enable a setting that allows fallback to unencrypted SMS/MMS messaging if the user or a Signal contact is offline.

^On iOS, the local message database is encrypted by the operating system if the user has a password on their lock screen.

^iMessage allows users to send instant messages to other iMessage users, as well as SMS/MMS messages to contacts who are not iMessage users. Only instant messages sent to other iMessage users are end-to-end encrypted. iMessage also contains an optional setting that allows fallback to unencrypted SMS/MMS messaging if the user or an iMessage contact is offline.

^Only messages between Viber users with the latest version for Android, iOS, Desktop or Windows 10 are end-to-end encrypted. The Windows Phone and BlackBerry versions are not supported.

^ abcLee, Micah (2 March 2015). "You Should Really Consider Installing Signal, an Encrypted Messaging App for iPhone". The Intercept. First Look Media. Retrieved 12 January 2016. Apple’s iMessage ... employs strong encryption, but only when communicating between two Apple devices and only when there is a proper data connection. Otherwise, iMessage falls back on insecure SMS messaging. iMessage also lacks forward secrecy and inspectable source code.

^"Requirements for enhanced security features". Viber Security FAQ. Viber. n.d. Retrieved 16 July 2016. Note that Viber for Windows Phone 8 will not support the new security features. It will continue to secure calls and messages through standard encryption methods.

^"Are my group chats encrypted as well?". Viber Security FAQ. Viber. n.d. Retrieved 16 July 2016. A group conversation will only use the upgraded security methods if all group participants are using the upgraded version of Viber.